Design of microwave hyperthermia instrument control system based on ARM embedded system

introduction

With the development of science and technology, various medical equipment have been introduced and widely used. The principle of microwave treatment of diseases is relatively complex. According to the current research results at home and abroad, microwave treatment of diseases is mainly achieved through thermal effect and biological effect. Due to the magnetic resistance between polar molecules, the oscillation is damped, thereby consuming microwave energy and generating heat. The purpose of curing the disease is achieved by using this heat, which is the thermal effect of microwave treatment. Through research and experiments, it is shown that the treatment effect of irradiating the lesion with microwaves far exceeds that of other hot compress methods. Most of the components of the human body are carbohydrates, and the molecules of carbohydrates are polar molecules. Under the action of microwave fields, polar molecules change their polarity with the microwave frequency, which is called polar oscillation. The frequency of polar oscillation is the same as the microwave frequency, and its amplitude is proportional to the microwave intensity. As we all know, Chinese medicine can treat colds and local inflammations through hot compresses and acupuncture; through the body's own heat, the body's own immune function can be achieved. Microwave refers to electromagnetic waves with a frequency of 300MHz-300GHz. It is the abbreviation of a limited frequency band in radio waves, that is, electromagnetic waves with a wavelength between 1 meter (not including 1 meter) and 1 millimeter. It is a general term for decimeter waves, centimeter waves, millimeter waves and submillimeter waves. The frequency of microwaves is higher than that of ordinary radio waves, and is also commonly referred to as "ultra-high frequency electromagnetic waves". As an electromagnetic wave, microwaves also have the dual nature of wave and particle. The basic properties of microwaves are usually presented as three characteristics: penetration, reflection, and absorption. For glass, plastic and porcelain, microwaves almost pass through without being absorbed. For water and food, they will absorb microwaves and make themselves hot. For metal objects, microwaves will be reflected.

Microwave therapy is a medical device that uses the biological characteristics of microwaves to treat various diseases. It integrates high-tech technologies such as microwaves, sensors, automatic control, computer software and hardware. Most of the control systems of microwave therapy devices on the market are implemented with single-chip microcomputers, which generally have the disadvantages of cumbersome operation, no graphical operation interface, and non-intuitive display. As an emerging marginal discipline, bioelectromagnetism has been increasingly valued by relevant experts and scholars outside China. The research on high-frequency electromagnetic waves has been extended to the millimeter wave band and is regarded as the focus of research. The research on millimeter wave biomedical engineering began in the 1960s. In 1968, Canadian scholar Webb published the first article on the biological effect of millimeter waves on inhibiting bacterial growth. Later, he reported that microorganisms have energy absorption resonance points similar to resonance for millimeter waves, and pointed out that normal cells and cancer cells have different absorption resonance points for millimeter waves. Since then, many scientists in Russia, the United States, Germany, France and China have done a lot of basic experimental research and clinical verification work. The results show that low-energy-density millimeter wave irradiation can cause obvious biological effects, and a large amount of valuable data has been accumulated on the clinical application of millimeter waves. As a type of millimeter wave, microwaves not only have the common characteristics of millimeter waves, but also have some unique properties that are different from other millimeter waves. The main characteristics of microwaves are their light-like properties, penetrating properties, and non-ionizing properties.

ARM (Advanced RISC Machines) is a well-known company in the microprocessor industry. It has designed a large number of high-performance, low-cost, low-energy RISC processors, related technologies and software. The technology has the characteristics of high performance, low cost and low energy consumption. It is suitable for a variety of fields, such as embedded control, consumer/educational multimedia, DSP and mobile applications. Since ARM embedded technology can miniaturize the control system, and the developed products are powerful, low-cost and have a high cost-performance ratio. Therefore, according to the market needs of microwave hyperthermia, we have developed a new type of microwave hyperthermia based on ARM embedded system and configured with WINCE.NET operating system.

1 Hardware System

1.1 Hardware Function Introduction

Microwave knife is a microwave scalpel that uses microwave energy for surgical operations. It consists of a microwave power source with a frequency of 2000-10000 MHz and a power of 70-150 W, which is continuously adjustable and connected to the surgical knife through a transmission line. The energy generated by the microwave source enters the patient's surgical site along the surgical knife through the transmission line to achieve the purpose of the operation. It has the characteristics of good hemostasis, no carbonization of the blade, sterilization, prevention of surgical infection, etc., and is small in size and flexible in operation. Ablation technology is a technology that allows the microwave treatment source to pass through the natural cavity of the human body, accurately intervene in the local lesion site of the human body, and automatically and accurately control its treatment power, time and treatment range.

The microwave transmitter of this system can be connected to a microwave knife and ablation needle. The working conditions are as follows:

(1) Microwave knife: When the microwave knife is used during surgery, the user controls the output power of the microwave knife through the human-computer interaction interface. At the same time, the system automatically accumulates the operating time of the microwave knife to facilitate medical record recording.

(2) Ablation needle: When the ablation needle is used for thermal therapy, the user can pre-set the ablation needle operating power, time and warning temperature. The system uses a countdown method to calculate the ablation needle operating time. After the time returns to zero, the system automatically cuts off the power output. During the treatment process, in order to prevent the temperature of the patient's treatment area from being too high and causing tissue damage, the system can also monitor the temperature changes of the affected area. When the detected temperature is higher than the warning temperature, the system automatically lowers the output power of the ablation needle; when the detected temperature returns to normal, the system restores the output power of the ablation needle to the pre-set value.

1.2 Hardware Composition

The whole hardware system is divided into three parts, namely, embedded system module, temperature acquisition and control module and microwave source. Figure 1 is the hardware structure diagram of the system.

Figure 1 Hardware system structure diagram

Figure 2 Embedded system module structure diagram

1.2.1 Embedded System Module

The structure of the embedded system module is shown in Figure 2. The module uses Samsung's ARM9 series microprocessor S3C2410, which includes 64M RAM and 64M Flash. The embedded system module is connected to a Sharp 10.4-inch LCD display. The embedded system is a "device used to control, monitor, or assist the operation of equipment, machinery or plants." It can be seen that the embedded system is a combination of software and hardware, and can also cover mechanical and other auxiliary devices. At present, a generally recognized definition in China is: a special computer system that is application-centered, based on computer technology, with tailorable software and hardware, and adapts to the strict requirements of the application system on function, reliability, cost, volume, and power consumption. Its resolution is 640×480, and it serves as the system's human-computer interaction platform for user operation.

The embedded system module is the core control part of the whole system. It provides a friendly human-computer interaction interface for users to set parameters such as power, time and warning temperature, and then communicates with the microcontroller through the serial port to control the output power of the microwave source and display the real-time temperature curve on the LCD. The embedded system is a special computer system that is application-centric, based on computer technology, with tailorable software and hardware, suitable for application systems, and has strict requirements on functions, reliability, cost, volume, and power consumption.

1.2.2 Temperature acquisition and control module

The temperature acquisition and control module consists of a single-chip microcomputer and a temperature acquisition circuit:

(1) Single-chip microcomputer. The single-chip microcomputer uses the C8051F005 chip from Silabs, which has built-in 12-bit A/D and 12-bit D/A converters. It collects 8-channel temperature signals through A/D and sends them to the embedded system module through the serial port. At the same time, it converts the power value transmitted from the embedded system module into voltage through D/A to drive the microwave source.

(2) Temperature acquisition circuit. During the thermal therapy process, in order to detect the temperature changes of the affected part of the human body, the system is equipped with a temperature acquisition circuit. It consists of 8 thermistors and a signal amplification circuit. The thermistor is first divided by a fixed resistor, and then amplified by the signal amplification circuit and connected to the A/D converter of the microcontroller.